Rated 4 out of 5 stars

per David Mahaffy el set. 7, 2010 · enllaç permanent

For those (like me) desperate for Buttons! in TB 3.1.2, I unzipped the XPI, modified the max version in the install.rdf file, re-zipped it, and it seems to be working. I've put a copy of the modified XPI at
http://tech-meanderings.blogspot.com/2010/09/buttons-tweak-for-thunderbird-31x.html if you want to try it.